Thermoplastic materials, such as hot melt adhesives, are used in a variety of applications including the manufacture of diapers, sanitary napkins, surgical drapes and various other products. The technology has evolved from the application of linear beads or fibers of material and other spray patterns, to air-assisted applications, such as spiral and melt-blown depositions of fibrous material.
One type of known intermittently operable liquid dispensing system includes one or more dispensing modules for applying liquid material in an intended deposition pattern from respectively associated modules. These modules include valve components that permit the individual modules to operate in an on/off fashion. One example of this type of dispensing module is disclosed in U.S. Pat. No. 6,089,413, assigned to the assignee of the present invention. The module includes valve structure that changes the module between on and off conditions. In the off condition, the module enters a recirculating mode. Three-way versions of these modules have a recirculating mode that redirects the pressurized material from the liquid material inlet of the module to a recirculation outlet which, for example, leads back into a supply manifold and prevents the material from stagnating. Other two-way modules, without recirculation, have also been used to provide selective metering and/or on/off control of material deposition. Another type of liquid dispensing system, referred to as a continuous applicator, includes a plurality of liquid dispensing nozzles or dies for dispensing liquid material to a substrate, wherein all the nozzles are simultaneously controlled such that all the nozzles are either on or off.
Various liquid dispensing systems have been developed that can accommodate varying numbers of modules. Different types of dispensing modules, or similar modules having different dies or nozzles, may be used with these systems so that a variety of deposition patterns across the applicator may be applied to a substrate. The most common types of air-assisted dies or nozzles include melt-blowing nozzles and dies and spiral nozzles. Pressurized air is used to either draw down or attenuate the fiber diameter in a melt-blowing application, or to produce a particular deposition pattern in other applications, such as when using spiral nozzles. When using hot melt adhesives or other heated thermoplastic materials, the process or “pattern” air may be heated so that it does not substantially cool the thermoplastic material prior to deposition on the substrate.
An exemplary applicator that allows users to tailor the applicator to specific needs is shown and described in U.S. Pat. No. 6,422,428, commonly assigned to the assignee of the present invention and hereby incorporated by reference herein in its entirety. This applicator comprises multiple manifold segments and associated liquid dispensing modules secured to the manifolds segments. Manifold segments may be selectively added or removed from the applicator to optimize the spray performance of liquid material dispensed from the respective liquid dispensing modules.
When different types of liquid dispensing modules are used on a single dispenser, or when different types of nozzles or dies are used with the modules on a multi-module dispenser, it may be desirable to control the process air provided to individual modules or nozzles so that the performance of each module or module/nozzle combination is optimized. Pending U.S. patent application Ser. No. 10/282,573 and pending U.S. patent application Ser. No. 10/836,765, each of which is assigned to the assignee of the present invention, disclose various embodiments of liquid dispensing systems having a plurality of liquid dispensing modules for dispensing liquid material. These systems include controls between an air supply and the liquid dispensing systems to control the flow rate and/or flow rate of process air provided to individual modules. In some applications, it may be desirable to control process air at points in the system that are closer to locations where process air exits the individual nozzles or dies. This application discloses various embodiments of liquid dispensing systems wherein process air provided to one or more modules or nozzles is independently regulated by controls provided at locations other than between an air supply and the liquid dispensing system.